JavaScript lacks an API to fetch the time zone setting of the user's operating system. Often, when developing web applications, it is desirable to know the user time zone so that server code can accurately adjust UTC dates into the user's local time when passing data or rendered html back to the browser. The most common approach to this problem is to fetch the UTC offset for the current date, and use that value to look up a time zone name in a list of time zones keyed by offset. This approach, however, fails to properly account for daylight savings time (DST) changes, and also fails to distinguish hemispheric differences in DST rules. For example, New Zealand time zones observe a daylight savings time, but do so during southern hemisphere summer (September-April). As a consequence, applications using any northern hemisphere time zone for clients in New Zealand would display inaccurate times for part of the year.